308 gt4 Timing set up on single distributor model

Does anyone know how to set up the timing on my 308gt4 with 'single' distributor.

My WSM specifies how to set up timing on the twin distributor model only, as follows: Set timing at idle (850 rpm) to 6deg BTDC. The microswitch under the accelerator earths out the first set of points as soon as the peddle is depressed, the second set of points govern the timing from then on. The second set of points are further advanced and the result according to the manual is that the timing advance will be 16deg BTDC at about 1100 rpm (only just above idle). It also states that the advance mechanism will increase this to 34deg BTDC at 5000rpm. Then of course repeat the whole process for cylinders 5-8 at the corresponding flywheel marks. The reason for two sets of points was something to do with low emmissions at tickover or something?

On investigating my car it appears to me that on the single distributor model the second set of points governs cylinders 5-8 and does not act as an instant 10deg advance. Therefore I am assuming that when I press down on the accelerator peddle I am not hitting any microswith and immediately advancing my timing to 16deg BTDC?

I recently adjusted valve seats and rebuilt the distributor. I set the timing at the 6deg mark on tickover as per the manual without really thinking it through. When I checked the advance at 5000rpm it was not reaching the 34 deg mark.

As there is only a limited amount of timing adjustment possible on any given spline, I need to get a half decent static time set up before I can strobe it in accurately. So how do I do it??

I read in a recent post of 'Harry' that he had is timing set at a dyno tuning shop to 34 deg at 5000 and it resulted in an advance of about 11deg at idle. Should I start with a static time to the 16 deg mark, or the 6deg, Or somewhere in between?

Anyhelp would be appreciated! It is worth noting that the car runs and drives well but feels under powered in it's present set up, which I am now convinced is wrong!

The timing was set at 34 deg@5000rpm at both dists, idle timing was a result from that. The mechanic measured idle timing just as a reference, he said he does not like too 'late' idle timing anyhow and about 20 deg dynamic advance are fine.

Regards
Harry

There are actually 3 different advance curves on carb 308s so the first thing to decide is which one your car should have. (Only 2 used on US cars I think.) Single distributor models not only lack the microswitch setup but actually have a slightly different advance curve (compared to euro twin distributor models). Actually it's not so simple because us and euro twin distributor models have different setups.

I'm assuming you have a us model -it sounds to me like your car has the S127G distributor which should be set as follows:

Firstly, the positioning of the distributor splines into the cam is easy. Turn the engine to TDC. Remove the distributor cap and you will notice a small notch in the body (might still have a bit of red paint in it!) and a line on one of the electrodes of the rotor arm. Line these up as close as you can. Just turn the engine a whole rotation if it's 360 deg out of course.) This gives you the correct alignment of the distributor splines in the cam and very approximately the right ball park for the timing. Often you'll fall on the mid range of the adjustment of the distributor in its slots but if not, just make sure that you have a bit of scope of adjustment left on the slots.

The timing should be set with a strobe at 6-7 deg BTDC at 900 rpm.

When this is done, speed up the engine and check the following:

The ignition should advance rapidly to 17 deg BTDC at 1800rpm (and return freely and rapidly to idle setting at 900 rpm.)

Ignition advance should advance from 1800 rpm in a linear fashion until max advance: 40 deg at 6000 rpm.


Those are factory specs for the single distributor model. I wouldn't do anything different from that.

For the single distributor model that does indeed correspond to 34 degrees btdc at 5000rpm (and about 33 deg for the euro twin distributor model). However if that gives you anything other than 6-7 degrees at 900 rpm, then the distributor needs looking at - they are very prone to wear although with patience you can play around with the shims and get the right curve.

Note that the factory advance curve for the twin distributor euro model gives more total advance 42 degrees at 6800 rpm. So, yes, the engine can take more advance but 1. that engine is a different spec (cams, exhaust) and 2., the advance curves are a real compromise so just because the euro twin distributor model is the most powerful, that doesn't make its advance curve more desirable for your car.

Another thing - comparing the different advance curves, there is a fair difference below 2000 rpm. The reason for this is that the most important thing is the fast advance needed to have enough advance at 2000 rpm for some power and not much at 900 for a well behaved idle (particularly with respect to emmissions). Models with a microswitch use the second set of points to achieve this rapid transition - models without the switch have an advance curve with a more rapid part from 900 to 1800 rpm. What's clear is that if your non-microswitch distributor is advancing a bit faster than it should low down, that's not a big problem. Another thing which is a bit more important is that there should be a very small amount of preload on the advance springs so that you're not getting any advance before 1100-1200 rpm. Again, that's so that you have a nice steady idle without any chance of the ignition advancing between 900 and 1000 rpm.

All the figures I have given are engine rpm and ignition advance measured at the crankshaft.

You can improve on the factory setup...... but only by going to a programmable ignition system.

Matt.

Thanks for all your help guys, I will go back and check my set up, thinking now that I got it pretty close first time.

Matthew, thanks for all the data, a real help. I will get the missus in the driving seat to hold those various rpms while I strobe the timing marks.

My car is a UK model not US by the way (although the picture under my user name is a US model) I Will check the various advances based on the figures you have given me so far and see where we're at. Do you have any other data on the UK spec? Cheers

Wayne - You're ok with the data I gave, it applies to UK single distributor cars as well as US cars.

Tell us how you get on with setting it up. It's easy but getting your assistant to hold the rpm steady at various points between 1000 and 3000 rpm is sometimes not so easy. Often 308s have a tendency to run lean on transition and if the carbs aren't set up nicely then holding steady rpm can be tricky..... and of course you want to get your ignition right before you start doing much with the carbs. Still, with patience (from the missus) you'll get there.

Matthew.